The purpose of this study is to determine the behavior and function of the pyloric sphincter. This objective will be accomplished through studies in man and in muscle, in vitro. The specific problems to be investigated are: (1) The physiological characteristics of the human pyloric sphincter; (2) The in vitro properties of pyloric sphincter muscle as compared to adjacent muscle; and (3) the role of the pyloric sphincter in the pathogenesis of gastric ulcer disease. To accomplish these objectives, intraluminal manometric recording techniques will be utilized in man. Normals and patients with gastric ulcer will be evaluated for their pyloric sphincter response to the endogenous release and exogenous administration of the gastrointestinal hormones. The pyloric sphincter will be evaluated as an antereflux mechanism. The in vitro behavior of the pylorus and adjacent muscle will be tested for its hormone dose-response characteristics, and hormonal interactions. In addition, the isometric length-tension and isotonic force-velocity properties of the muscle will be determined. These mechanical properties will be further evaluated in the presence of gastrointestinal hormones and neural transmitters. These studies will characterize the pyloric sphincter muscle in vitro and pyloric sphincter behavior in man, in vivo.